The invention relates generally to an rpm-to-voltage converter, and, more particularly, to an rpm-to-voltage converter for use in the open- or closed-loop control of operating characteristics of an internal combustion engine and a vehicle equipped therewith.
In the field of motor vehicles, the detection and processing of rpm pulses is of great significance. In addition to its importance in engine control, for instance for fuel metering and computing the instant of ignition, the detection of rpm is also necessary in anti-wheel-lock systems as well. The purpose then is to obtain a signal relating to the actual rpm as rapidly as possible.
Present-day rpm/voltage converters function with a monostable multivibrator, for instance, which is triggered in the rhythm of the rpm signals as they appear, and an analog value for the rpm is then produced by averaging the signals of constant duration as they appear.
A digital rpm/voltage converter is also already known, from German Offenlegungsschrift No. 23 36 015. In this known converter, the concept that the period duration of a pulse train is inversely proportional to its frequency is applied. If a counter is therefore caused to count downward from a high value in accordance with a hyperbolic function, and if this counting process is terminated at the onset of a new period, then the counter state is proportional to the frequency. It is illuminating that the converter product is all the more precise, the better the hyperbolic function of the downward-counting process is replicated. This, in turn, requires a non-inconsiderable expenditure for circuitry, so that for many applications, the known rpm/voltage converter (or more precisely, a frequency/binary digit converter) is too expensive.